Hippocrates was possibly the first person to record the benefits of white willow bark. He did so in the Fifth century BC. In 1828 a French pharmacist, Henri Leroux and an Italian chemist, Raffaele Piria, we are able to isolate a compound in the grayish brown bark from the white willow tree (Salix alba) known as salicin. Since then, salicylic acid, an active derivative of salicin has been further separated out and has found a home as one of the primary ingredients in aspirin.
In an effort to get bigger, better, faster, the body building industry popularized the concept of "stacking" or combining certain ingredients to take advantage of their synergistic effect. Synergy occurs whenever ingredients are combined and the specific combination of those ingredients provides a greater benefit than the individual benefits that could be realized if each of those ingredients were taken independent of each other.
For decades, the ECA stack reigned supreme for its popularity in the body building industry. This was a "stack" that combined Ephedra, Caffeine and Aspirin. Although the ratio of this combination varied, 25 milligrams of ephedra was commonly combined with 200 milligrams of Caffeine and 325 milligrams of Aspirin. Unfortunately, this combination became extremely hard to put together when the Food and Drug Administration (FDA) banned the sale of all dietary supplements containing ephedra on February 6th, 2004. Despite numerous studies demonstrating the safety of ephedra in controlled doses, the FDA would not budge on their finding that ephedra posed an "unreasonable risk of illness or injury." On August 17th, 2006, after being challenged in a federal appeals court, the FDA upheld the ephedra ban with a 133,000 page report citing 19,000 individual adverse reactions. In the wake of this dilemma, ephedra alternatives were quickly located to combine with caffeine and aspirin.
Conceptually, the ECA stack effectively assists with weight loss and energy gain. Certain stimulants, such as ephedra are known to be "beta agonists", meaning they function as keys on a certain gene in the body (by targeting the "beta-2 adrenergic receptor" or "ADRB2") to unlock a genetic response. Three responses that are believed to be unlocked are increased levels of norepinephrine, increased levels of epinephrine and increased levels of cyclic adenosine monophosphate (cAMP).
Norepinephrine and epinephrine are quite similar. Both are common neurotransmitters in the brain that also function as hormones in the body. As norepinephrine levels and cAMP levels increase, heart rate increases and the release of glucose is triggered from stored energy in the body. When taken in a stack with caffeine and aspirin, this chain of events increases blood flow to muscle tissue and increases body temperature, creating a thermogenic effect on the body. It is also believed that during this process, the body begins burning white adipose fat tissue, appetite becomes suppressed, and fatigue is reduced as energy levels increase.
When a stack of stimulants and aspirin (or white willow bark) enter the body, a little light goes off (not literally) telling the body that it was just stimulated as the metabolism begins increasing. In response, the body begins producing phosphodiesterase inside your cells and prostaglandins outside your body's cells. Both of these reactions lower cAMP levels, slowing the metabolism boost from the ECA stack.
Caffeine prevents cAMP levels from decreasing by blocking the production of phosphodiesterase inside cells, while further increasing the body's production of epinephrine, which again helps raise cAMP levels. Aspirin (or white willow bark) prevents cAMP levels from decreasing by blocking the production of prostaglandins outside the body's cells. Through these specific actions of caffeine and aspirin (or white willow bark), thermogenesis is sustained for longer periods of time while the metabolism is held at a higher rate, allowing the body to burn more calories longer.
Taking this combination of ingredients prior to exercise should also help with a better work out, as the body will not get fatigued as quickly and muscles will recover and feel fresh faster. All that being said, please remember that your body is not designed to burn stored fat as fuel, if you are eating more calories each day than your body is burning as fuel. Taking a dietary supplement may help your body burn more calories, but do not expect dramatic, long-term changes in your body shape without also making lifestyle changes to your eating and exercise habits.